Like other posters, I have had many mammograms and never once has anyone asked for my consent before touching me and manipulating my breasts into the correct position. Agreeing to the appointment and turning up is you giving consent.
Surely this is not always the case? With other procedures I've definitely been asked for consent. Turning up wasn't enough!
I googled anything I was unsure of so as to be best prepared and know exactly what to expect.
I've done the same but have still been caught out by things not covered in what I'd read, or by things being different at my hospital. And sometimes a hospital will include notes with an appointment letter & you get there & find things are different from their own notes.
You have a voice and if you were uncomfortable with the treatment you were receiving, you should have said something, even just to tell her to stop and ask to see someone else.
Sometimes & for some people, this is just too difficult. Reasons might include: shyness, being unsure whether the procedure is being done wrongly (it was OP's first mammo), not wanting to make a fuss or be seen as difficult, fear of repercussions, fear of being seen to 'waste' an NHS appointment, not knowing your rights, fear of taking more time off work for another appointment, etc.
I'm willing to cut the OP some slack on this. I'm surprised others aren't.